1. Field of the Invention
The present invention relates generally to a submicron disc filter in use for filtering various chemicals, pure water and various gases, and more particularly to an improvement in such a submicron disc filter having a filter element constituted by superposing a plurality of filter units each including a support member and filter membranes.
2. Description of the Prior Art
In connection with filtering various pharmaceuticals, chemicals and gases in use for production of electronic parts, and pure water used in food industry, such filters are required to have chemical-resistance, heat-resistance, and a filter precision of submicron order. Accordingly, a variety of submicron disc filters for such ultrafiltration have been proposed and used. One of such submicron disc filters is configured as follows: The filter consists of a filter element housed in a casing. The filter element includes a plurality of superposed filter units. The filter unit is constructed of a disc-type annular support member whose major parts on its both sides or surfaces are covered with porous filter membranes for ultrafiltration. Each support member is constructed of upper and lower counterparts which are secured to each other. Each counterpart is of the type of a grid to support the filter membrane thereon. Additionally, fluid flow passages are formed between the upper and lower counterparts so that filtrate after filtration with the filter membrane flows along the fluid flow passages to an axial fluid flow passage formed axially in the filter element.
However, in such a submicron disc filter of the above-mentioned construction, the structure of each support member for the filter membranes is considerably complicated and therefore difficult to produce. In this connection, high precision is required in production of the support member counterpart because the two support member counterparts are fitted with each other to form a support member. Additionally, such a structure unavoidably inceases the thickness of each support member, so that it is difficult to increase the number of filter units of the filter element in a casing having a limited volume. This makes it difficult to increase the filtering area of the filter element, thereby allowing pressure drop increase and filter life shortening. Furthermore, since the surface of the support member is grid-shaped, angular corners and edges tend to be formed on the support member surface on which the considerably thin and soft filter membrane is supported receiving fluid pressure of the fluid to be filtered. Accordingly, when a high fluid pressure acts on the filter membrane particularly in th event that clogging proceeds, concentrated stress is generated at the angular corners and edges, thereby stretching the filter membrane to enlarge the pore size thereof or to tear the filter membrane.